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HER2-positive breast cancer represents 15%-20% of breast malignancies and is characterized by an aggressive behavior and high recurrence rates. Anti-HER2-directed agents represent the mainstay of treatment of patients with HER2-positive metastatic breast cancer (MBC). In this review we propose a treatment algorithm for patients with HER2-positive MBC based on the currently available literature on the topic. The combination of trastuzumab, pertuzumab and a taxane (THP) remains the preferred first-line therapy in most scenarios. Results of trials recently presented at the European Society for Medical Oncology (ESMO) Congress 2021 might have direct clinical impact in the second- and later-line settings. The randomized DESTINY-BREAST03 study compared trastuzumab deruxtecan (T-DXd) with trastuzumab emtansine (T-DM1) in patients previously treated with trastuzumab and a taxane. T-DXd significantly improved progression-free survival and showed a trend towards improved overall survival, establishing this agent as preferred second-line therapy. Treatment with T-DM1, or the combination of tucatinib, trastuzumab and capecitabine, are considered reasonable options after second-line therapy. For subsequent lines, trastuzumab duocarmazine, neratinib plus capecitabine or the continuation of trastuzumab with different chemotherapy partners are valid options. For patients experiencing disease relapse up to 6 months after completion of adjuvant therapy, as well as for those relapsing within 12 months from the completion of pertuzumab-based adjuvant treatment, we recommend T-DXd as preferred first-line option. For those relapsing between 6 and 12 months after non-pertuzumab-based adjuvant treatment, we recommend first-line THP. Finally, for patients with active brain metastasis, tucatinib-based combination represents a suitable second-line option., Highlights • Treatment landscape for patients with HER2-positive metastatic breast cancer is rapidly evolving. • Trastuzumab deruxtecan improved outcomes in comparison with T-DM1 and should now be the preferred second-line therapy. • T-DM1 and tucatinib-based therapy are valid third-line options. • Toxicity profile should be taken into account when considering different later-line treatment options.

Brain metastases (BMs) are frequent events in patients with HER2-positive metastatic breast cancer (MBC) and are associated with poor prognosis. Small-molecule anti-HER2 tyrosine kinase inhibitors (TKIs) are promising agents for the treatment of BM. In this study, we assess the clinical outcomes of patients with HER2-positive MBC and BM treated with TKI-containing regimens compared with those treated with non-TKI-containing regimens.PubMed, Embase, Cochrane Library, and conference proceedings (ASCO, SABCS, ESMO, and ESMO Breast) were searched up to June 2021. The primary endpoint was progression-free survival (PFS) in patients with BM. Secondary endpoints included PFS in patients without BM and overall survival (OS). The study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Overall effects were pooled using random-effects models.This systematic review and meta-analysis included data from 2437 patients (490 with and 1947 without BM at baseline) enrolled in five trials assessing tucatinib-, lapatinib-, pyrotinib-, or afatinib-based combinations. A nonstatistically significant PFS benefit favoring TKI-containing regimens was observed in both patients with BM [hazard ratio (HR) 0.67, 95% confidence interval (CI) 0.41-1.12; P = 0.13] and without BM (HR 0.55, 95% CI 0.24-1.26; P = 0.16). Sensitivity analysis, excluding each study singly, demonstrated a significant PFS benefit favoring TKI-containing regimens in patients with BM after the exclusion of afatinib from the analysis (HR 0.56, 95% CI 0.35-0.90; P = 0.016). No statistically significant differences in OS were observed between the comparison groups.A trend in PFS favoring TKI-containing regimens was observed in patients with BM. Sensitivity analysis including only trials that evaluated regimens containing tucatinib, lapatinib, or pyrotinib demonstrated a significant PFS benefit favoring TKI-containing regimens in patients with BM.